SiAlON materials have a number of uses such as, for example, cutting inserts for various metal cutting application and wear parts for various wear applications (e.g., plunger rods for pumps, plunger ball blanks, down hole pump check valve blanks, bushings, blast nozzles, and other wear and impact applications).
Ceramic materials have also been used in high temperature wear applications in structures like, for example, microturbines. In the microturbine applications, the ceramic materials may comprise the stator (i.e., the stationary blades), the rotor (including the rotor blades), the fuel injector nozzle, and the shroud. These components of the microturbine require adequate high temperature creep resistance and adequate high temperature deformation resistance.
Exemplary patents that disclose SiAlON materials are U.S. Pat. No. 4,563,433 and U.S. Pat. No. 4,711,644. One article that discusses SiAlON materials is Izhevskiy et al., “Progress in SiAlON ceramics, Journal of the European Ceramic Society 20 (2000) pages 2275–2295.
SiAlON materials may contain an alpha prime (or alpha′) phase and a beta prime (or beta′) phase and one or more other phases such as, for example, a glassy phase and/or a crystalline phase. The alpha prime SiAlON phase may be of the formula MxSi12−(m+n)Alm+nOnN16−n where M is Li, Ca, Y or other lanthanides and where the theoretical maximum of x is 2, the value of n ranges between greater than 0 and less than or equal to 2.0, and the value of m ranges between greater than or equal to 0.9 and less than or equal to 3.5. The beta prime SiAlON phase may be of the formula Si6−zAlzOzN8−z where 0<z≦4.2. In the case where M is yttrium, the crystalline phases may include YAG (yttrium aluminum garnet) which is a cubic phase of the formula Y3Al5O12); YAM which is a monoclinic phase of the formula Y4Al2O9; N-YAM which is a monoclinic phase of the formula Y4Si2O7N2; and Y—N-α-Wollastonite which is a monoclinic phase of the formula YSiO2N.
SiAlON materials may comprise an alpha prime SiAlON phase and a beta prime SiAlON phase, as well as further contain silicon carbide particles dispersed throughout the SiAlON matrix. Such a SiAlON material is disclosed in U.S. Pat. No. 4,826,791 to Mehrotra et al.
Other ceramic materials include an alpha prime SiAlON phase, a beta SiAlON phase and an intergranular phase wherein the ceramic optionally contains refractory phases. The ceramic material has an alloyed surface with a higher oxygen and aluminum content. U.S. Pat. No. 4,880,755 to Mehrotra et al. discloses such a ceramic material.
U.S. Pat. No. 5,370,716 to Mehrotra et al. discloses a high Z-SiAlON material comprising beta prime SiAlON phase. The beta prime SiAlON phase has a formula Si6−zAlzOzN8−z where 1<z<3.
U.S. Pat. No. 5,908,798 to Chen et al. discloses a SiAlON material wherein the focus is on the reinforcement of alpha prime SiAlON with elongated grains of alpha prime SiAlON. The examples that include ytterbium produce a material with only alpha prime SiAlON phase that does not contain any beta prime SiAlON phase.
U.S. Pat. No. 6,124,225 to Tien et al. focuses upon the use of gadolinium (Gd) in a SiAlON material to produce an alpha prime SiAlON material that is reinforced by elongated grains of alpha prime SiAlON.
Although current SiAlON cutting inserts exhibit acceptable properties (e.g., hardness, toughness, thermal shock resistance) it would be desirable to provide for an improved SiAlON material that has application as a cutting insert that exhibits improved metal cutting performance properties including hardness, Young's modulus, toughness, thermal conductivity, and thermal shock resistance. The same is true for SiAlON wear parts in that although current SiAlON wear parts have acceptable properties (e.g., hardness, Young's modulus, toughness, thermal conductivity, and thermal shock resistance), it would be desirable to provide an improved SiAlON material that has application as a wear part that exhibits improved properties.